Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already cover the safety profile (readOnlyHint=false, idempotentHint=true, destructiveHint=false), and the description adds the critical non-structural fact that only the UI invokes this, not the agent. It does not state what happens on duplicate events or errors, but idempotency is already declared in annotations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two short sentences, front-loaded with scope and ending on the strongest constraint ('Never call it yourself'). Nothing redundant or padded.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema needed (it is a fire-and-forget event recorder), a fully documented schema, and clear annotations, the description supplies what an agent needs. It could say more about error or duplicate-event behavior for a caller, but for an agent that should never call it, that gap is minor.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, and every parameter (event enum, offer_id, card_token, contact_email) is fully described in the schema with patterns and provenance. The description adds no parameter meaning beyond that, so the baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb and resource: recording an offer card 'shown' or 'accepted' event, and explicitly scopes it to HumanFn's offer card UI. It distinguishes itself cleanly from siblings such as accept_human_function_offer by declaring that the UI, not the agent, is the caller.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

It gives an unambiguous when-not rule ('Never call it yourself') plus the only valid caller ('Used only by HumanFn's offer card UI'). An agent reading this knows immediately to route accept actions through accept_human_function_offer instead of this tool.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.